Intramedullary nails and the like have been used by surgeons for many decades to set bone segments for healing, such as when setting a fractured femur or radius. Terms used for these types of devices include intramedullary nails, rods, pins, Nancy nails, Ender nails, Elastic Stable Intramedullary Nails (ESINs) and Titanium Elastic Nails (TENs.) These devices typically extend along at least a portion of a medullary cavity of a bone in a generally axial direction. Some intramedullary nails are rigid, fill all or most of the medullary cavity of a bone, and can include interlocking parts. Other nails are much more slender and flexible, and fill only a small portion of the cross-section of the medullary cavity. Flexible nails provide the benefit of entering the medullary cavity of a bone away from the growth plate in children with fractures and other bone destabilizing conditions, as opposed to rigid nails which generally traverse, and thus may injure the growth plate.
An example of a flexible type of intramedullary nail is provided by U.S. Pat. No. 4,169,470 issued Oct. 2, 1979, to Josef Ender et al. Ender et al. teach the use of a nail having a length predetermined for a particular application according to an individual patient's anatomy and fracture pattern. In some procedures, more than one nail is used to set a bone. As such, a large variety of nail lengths must be on hand during a surgical procedure using such nails. Additionally, estimating or pre-measuring the correct nail length is frequently challenging, particularly with displaced fractures. In some procedures, the surgeon may not know the desired length until a nail is inserted and it is determined to be too long or too short for the particular application. This results in some nails being discarded, and can require a large inventory of nails to be on hand for every procedure. For example, a variety of nails are often provided in 1 cm increments. Smith & Nephew lists 18 different nail lengths that must be stocked. This is multiplied by 3 or 4 when various incremental diameters are needed, such as 3.0, 3.5, 4.0 and 4.5 mm. In some procedures a trial pin is first placed and its insertion depth is measured to determine the proper nail length for the procedure. This approach requires an extra step, and in some cases the replacement nail does not follow the same path through the bone segments as does the trial pin. This can require additional attempts to place the nail, or leave a nail in place that is not the ideal length.
Ender et al. disclose nails that include a slot at one end. Ender et al. teach that these slots can be used to place an extraction hook used for later removal of the nail. However, surgeons have subsequently used these slots to pass a bone screw therethrough for securing the end of the nail to the bone, as shown in FIG. 1. This method of securing is prone to screw thread stripping, such as when an operator over-tightens a screw when desiring more secure fixation, or when bone thickness or density is insufficient to hold the bone screw. Since the nail slot is elongated, in some instances the bone screw may not completely eliminate axial movement of the nail after implantation. The screw can toggle, causing loosening, breakage or pull-out of the screw. These events can cause the fracture to shift post-operatively, leading to sub-optimal results which may require revision.
Additionally, the nail end and bone screw head sit on top of the outer bone surface and can interfere with surrounding tissue, causing prominent, palpable and painful implants, and or other undesirable side effects. This is done to prevent the end of the nail from being buried and covered by healing bone, making extraction difficult. Resulting pain from such an implant prominence can lead to a patient refusing to bend a joint until the implant is removed, adding further delay to patient recovery.
Another example of a flexible intramedullary nail is provided by U.S. Pat. No. 8,979,846 issued Mar. 17, 2015, to Navin Thakkar. Thakkar teaches the use of a universal length nail that may be cut to the desired length after implantation. With the excess length of the nail protruding from the bone, a surgeon can cut the nail at a distance of about 1 cm from the external surface of the bone at the entry point. This leaves about 1 cm of the nail protruding from the bone until such time that the nail is removed, which can cause undesirable side effects such as those described above in reference to Ender.
In some embodiments disclosed by Thakkar, neither end of the flexible nail is anchored to the bone. In other embodiments, multiple nails are placed through the greater trochanter of a femur and anchored thereto using a proximal fixation device. Such a procedure is not performed these days. Today, whenever a rod is sent through the greater trochanter, it is virtually always a single, larger (8-10 mm) diameter rod in a person over age 13 (close to skeletal maturity), where violation of the greater trochanteric growth plate is not an issue. If the Thakkar construct were used to anchor nails to the greater trochanter, it is not clear that the construct would prevent the hooked ends of the nails from migrating outwardly from the bone.
DePuy Synthes Trauma, a division of Synthes GmbH, currently markets an elastic stable intramedullary nailing (ESIN) system having a Titanium Elastic Nail (TEN) or Stainless Steel Elastic Nail (STEN) Like the Thakkar nails, the Synthes nails are designed to be cut to length in situ. In some implementations, an externally threaded end cap is provided to reduce irritation of the protruding nail and help anchor a nail to the bone. The end cap is inserted over the cut end of the nail and threaded into the bone obliquely. It appears that this arrangement inhibits a fracture from foreshortening but does not provide any rigid fixation, and may not prevent the fractured bone segments from separating as the nail may slide out of the end cap. There is also no rotational control provided. At the date of this patent application filing, Synthes provides more information on the above systems in a surgical technique guide at: http://synthes.vo.llnwd.net/o16/LLNWMB8/INT%20Mobile/Synthes%20International/Product% 20Support%20Material/legacy_Synthes_PDF/DSEM-TRM-0115-0290-2_LR.pdf.
FIG. 2 of the present disclosure is a three-panel x-ray of a spiral fracture that was set with two prior art flexible intramedullary nails. FIG. 2A shows the untreated displaced fracture. This type of spiral fracture pattern is “length unstable.” FIG. 2B shows the fracture immediately postoperatively. FIG. 2C shows the fracture postoperatively after some time has elapsed and the protruding ends of the intramedullary nails have migrated out of the bone, allowing the bone fracture to foreshorten. This case illustrates the need for good anchoring of the entry site ends of the nails.
Indicated benefits of many prior art systems are quite limited. In light of the many challenges during surgery and postoperatively outlined above, what is needed and is not provided by the prior art are systems and methods that provide improved bone fixation with flexible intramedullary nails, including in skeletally immature children.